Pipe strings consisting of many pipe sections connected in tandem, are widely used in the sea to transfer crude oil and other hydrocarbons between the sea floor and a floating body, or between floating bodies. One common type of pipe string includes many steel pipe sections, each of a length such as 30 meters, that are connected together by threaded end portions lying at opposite ends of each pipe. Applicant notes that one type of thread is a helical thread, and another type includes axially-spaced circular threads. Each end of a pair of adjacent pipe sections is preferably sealed to the other pipe section by a sealing surface on the end of one pipe section that presses against a sealing surface on the end of the other pipe section as the pipe section are threaded together. Previously, the opposite ends of a pipe sections could not both be tightly scaled, unless very high precision were used in the manufacture which results in prohibitive cost.
Many fluids to be carried by the pipe string are highly corrosive. A protective coating or cladding can be applied to the inside surface of the pipe sections, and to adjacent pipe surfaces. The cost of applying such coating can be minimised by minimizing the area to be coated, especially areas that include sharp angles.
A pipe joint that includes a pipe with threaded portions and with sealing surfaces at the ends, often includes tongue and groove joints that lie beside sealing surfaces. There is occasional fracture of the steel pipe end at a side of the groove.